A sliding nozzle device is for example attached to a discharge outlet of a ladle, and controls a flow rate of molten steel by stacking two pieces of refractory plates that have a nozzle hole, and linearly sliding the lower plate with respect to the upper plate in a surface pressure loaded state, to vary an aperture of the nozzle hole.
Such a sliding nozzle device generally includes a fixed metal frame for holding an upper plate, a sliding metal frame for holding a lower plate and which slides linearly to slide the lower plate with respect to the upper plate, an opening and closing metal frame for holding the sliding metal frame in a slidable manner, an elastic body for loading a surface pressure between the upper and lower plates, and a driving device for driving the sliding metal frame. In this configuration, the sliding metal frame slides in a state in contact with the opening and closing metal frame under high pressure, and thus is in contact with the opening and closing metal frame via sliding members.
As such, the upper and lower plates are relatively moved slidingly in a state in which surface pressure is loaded, and are further used at high temperatures. Moreover, since the plate comes in direct contact with molten steel at an inner circumference plane of the nozzle hole during the casting, the temperature thereof becomes high as compared to its surroundings, and the plate expands around the nozzle hole. Among this expansion, the expansion along a nozzle hole center axis direction (molten steel flowing direction) is understood as causing damage on the plate. Namely, just the peripheral parts of the nozzle hole of the upper and lower plates come in contact with each other by the expansion along the center axis direction of the nozzle hole; this causes the plates to warp in opposite directions from each other, thus causing the surface pressure to concentrate on the nozzle hole surroundings. It is considered that damage such as chipping in the nozzle hole surroundings and surface roughness on the most important surface occur due to frequent sliding of the plates in order to change aperture of the nozzle hole, to control the flow rate in this state.
In order to prevent this damage, Patent Document 1 proposes to provide a depressed part around the nozzle hole of the plate. However, if the depressed part is provided as in Patent Document 1, there may be the risk of molten steel leakage from around the nozzle hole, depending on variation in use conditions such as a case in which the preheating of the plate is insufficient.
Meanwhile, known sliding contact systems with the aforementioned sliding metal frame in a sliding nozzle device include: a liner system in which metal liners are made in slidable contact with each other, and a roller system in which slidable contact is achieved by a roller.
In Patent Document 2, as one example of the former liner system, an opening and closing metal frame (cover housing) is disposed under a sliding metal frame (frame body), and two liners made of metal that extend in the sliding direction of the sliding metal frame are provided to each of the sliding metal frame and the opening and closing metal frame as sliding members. Namely, in this system, the two liners provided on either side of a center line of the sliding metal frame along the sliding direction comes into sliding contact with the liners on the opening and closing metal frame. However, in this system, the liners on the sliding metal frame and the liners on the opening and closing metal frame come in contact with each other in a slidable manner for the whole length of the slidable range of the sliding metal frame; thus, when the nozzle hole surroundings of the plate expand in the center axis direction of the nozzle hole as described above, this expansion cannot be absorbed, and damages occur such as the chipping in the nozzle hole surroundings and the surface roughness on the most important surfaces.
As one example of the latter roller system, Patent Document 3 discloses a system in which two rollers are provided on each side of a sliding metal frame (slide case) as sliding members, and the sliding metal frame is slid by having the opening and closing metal frame (surface pressure loaded member) serve as a rail. The main object of this system, is to reduce friction resistance by using the rollers and to make the size of the driving system compact. However, in this system, pressure from the opening and closing metal frame (surface pressure loaded member) is received just by the four rollers; in long term use, parallelism of the sliding plane thus cannot be secured due to wearing of the rollers or deformation of the roller shaft, and gaps readily generate between plate surfaces. This as a result causes problems that the plate wears and damages increase.
Since the plate comes into sliding contact under high temperature and high pressure in the sliding nozzle device as such, there is a problem that damages such as surface roughness and chipping of the nozzle holes readily occur, caused by for example the thermal expansion described above or the deformation of the device.